The present invention relates to a method of pattern formation which is utilized in the manufacture of semiconductor devices and the like.
Heretofore, the formation of a pattern in the manufacture of semiconductor devices, integrated circuits and the like has been mainly carried out in accordance with a photolithographic technique wherein a photoresist made of a photosensitive organic polymer resist material is utilized. However, as a result of advancements in recent semiconductor devices and the like, particularly in the field of large scale integrated circuits, the tolerances required for pattern formation have become very small as a result of reduction in the size of elements in a device and an increase of the packing density of elements. Other factors which require reduced manufacturing tolerances include the growing of nonplanar features of surfaces of elements, a diversification in the types of materials to be etched, the increased complexity of multilevel interconnection, and an increase in the ion-stopping ability which is required of a mask during ion implantation with an increased ion implantation energy. Thus, a photoetching technique in which a conventional organic polymer resist material is utilized is not capable of complying with the tolerance and other requirements mentioned above.
On the other hand, an inorganic resist material made as a laminate consisting of a selenium-based glass material layer and a silver layer or a layer containing a silver compound or silver in an alloy or the like has recently been developed (see U.S. Pat. No. 4,127,414). This inorganic resist material is of considerable interest because of its many excellent characteristics, including high resolution, which are superior to those of a conventional organic polymer resist material. However, even if photoetching is effected by the use of such an inorganic resist material as described above, it is required that the inorganic resist material layer be extremely this in order to obtain the high resolution characteristic. Accordingly, there still remains a problem in the application of such an inorganic resist material to a nonplanar substrate surface or metal layer. Furthermore, since optimum conditions such as exposure, development and the like differ in the case where a relatively large pattern is formed from the case where a fine pattern is formed, there is a problem in that the quality of the patterns deteriorates as a whole in the formation of a device having a relief which includes large and small patterns.
In this respect, U.S. Ser. No. 35,803 (or corresponding Japanese Laid-open Patent Application No. 149,941/1980 or European Patent Application Publication No. 0,018,653) "Process for fabrication of an article" as well as relevant papers "Bilevel high resolution photolithographic technique for use with wafers with stepped and/or reflecting surfaces" (J. Vac. Sci, Technol., 16(6), Nov./Dec. 1979, pp 1977-1979) and "Submicron optical lithography using an inorganic resist/polymer bilevel scheme" (J. Vac. Sci. Technol., 17(5), Sept./Oct. 1980, pp 1169-1176) disclose a bilevel resist prepared by laminating the above-mentioned inorganic resist onto an organic polymer layer as a kind of multilayer resist. Such a bilevel resist has the following advantages:
First, the flattening of a nonplanar substrate surface by means of the organic polymer resist material layer, and the formation of a fine pattern on a stepped or highly reflecting substrate by means of the inorganic resist are easily achieved to the high optic absorption of the resist. Furthermore, the formation of a thick polymer resist pattern having a rectangular section is also easy to achieve, and therefore, the aforesaid bilevel resist has a strong resistance which is required for the etching mask when performing reactive ion etching or ion beam etching working. The aforesaid process for the formation of the bilevel resist is also effective for forming a mask pattern for ion implantation.
However, there still remains a substantial drawback with the inorganic resist in bilevel resist during the formation of the pattern. Namely, the exposing and developing characteristics of the inorganic resist are different in the formation of a fine pattern from the formation of a comparatively large pattern. These characteristics can be adjusted such that when fine and larger patterns are separately formed, it is possible to make patterns of equivalent quality. In general, however, particularly in LSI, there are many cases in which these large and small patterns are both included. In forming a relief which includes such large and small patterns, the pattern formation of the above-mentioned bilevel resist is carried out under the same exposing and developing conditions of the inorganic resist in both types of patterns, resulting in either or both of the patterns being of unsatisfactory quality. As described above, a relief which includes large and small patterns cannot satisfactorily be formed by merely utilizing such bilevel resist.
In addition, difficulty in the alignment of a mask is an inherent problem with such a bilevel resist. In a projection exposure system, the automatic alignment of the mask is carried out by detecting light which is reflected by an alignment mark on the substrate. However, as described above, the most advantageous points of the bilevel resist in the flattening of a substrate surface and removal of the reflected light from the substrate. Therefore, no reflected light is obtained from the alignment mark covered with the bilevel resist, so that the above-stated automatic alignment of the mask is impossible. Furthermore, in such bilevel resist, the polymer layer and inorganic resist layer are always treated as an integral member, but neither of them is individually patterned. In other words, there has been no consideration of such bilevel resist in the prior art concerning its application to various pattern formations.
It is therefore an object of the invention to eliminate the above-mentioned disadvantages and to provide a method of pattern formation which is widely applicable, has various pattern forming functions, and by which a pattern with high resolution can be formed.
It is another object of the invention to provide a method of pattern formation by which a multilevel interconnection pattern can be formed by utilizing the organic polymer resist material layer in a two-layer resist as an interlayer insulation film or layer.
It is still another object of the invention to provide a method of pattern formation by which a thin film pattern according to a lift-off process can suitably be formed by utilizing a two-layer resist.